1-Alkanoylindoline-2-carboxylic acids and their 5,6-dihydroxy-derivatives, i.e., N-acylated Cyclodopaderivatives, are described in Nippon Kagaku Zasshi 87, 760 (1966) and U.S. Pat. No. 3,796,723 or Helv. Chim. Acta 53, 1701 (1970) respectively, e.g., as synthetical examples of O- and/or N-acylations. Also, 1-mercaptoalkanoylpyrrolidine-2-carboxylic acids and their functional derivatives are known, e.g., Captopril according to U.S. Pat. No. 4,105,776, as possessing antihypertensive activity. Surprisingly it was found that either by introduction of a mercapto group into the former indolines, or by expansion of the latter pyrrolidines to the indoline ring-system, superior antihypertensive agents are obtained.